Table of contents

1. Introduction to Genetics51m
2. Mendel's Laws of Inheritance3h 37m
3. Extensions to Mendelian Inheritance2h 41m
4. Genetic Mapping and Linkage2h 28m
5. Genetics of Bacteria and Viruses1h 21m
6. Chromosomal Variation1h 48m
7. DNA and Chromosome Structure56m
8. DNA Replication1h 10m
9. Mitosis and Meiosis1h 34m
10. Transcription1h 0m
11. Translation58m
12. Gene Regulation in Prokaryotes1h 19m
13. Gene Regulation in Eukaryotes44m
14. Genetic Control of Development44m
15. Genomes and Genomics1h 50m
16. Transposable Elements47m
17. Mutation, Repair, and Recombination1h 6m
18. Molecular Genetic Tools19m
- Genetic Cloning
  9m
- Methods for Analyzing DNA
  9m
19. Cancer Genetics29m
- Overview of Cancer
  21m
- Cancer Mutations
  7m
20. Quantitative Genetics1h 26m
21. Population Genetics50m
- Hardy Weinberg
  19m
- Allelic Frequency Changes
  31m
22. Evolutionary Genetics29m

6. Chromosomal Variation

Chromosomal Mutations: Aneuploidy

Genetics

6. Chromosomal Variation

Chromosomal Mutations: Aneuploidy

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2:49 minutes

Problem 11

Textbook Question

When cows have twin calves of unlike sex (fraternal twins), the female twin is usually sterile and has masculinized reproductive organs. This calf is referred to as a freemartin. In cows, twins may share a common placenta and thus fetal circulation. Predict why a freemartin develops.

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Understand the concept of a freemartin: A freemartin is a female calf that is sterile and has masculinized reproductive organs due to sharing a placenta with a male twin during development.

Recognize that in cows, fraternal twins often share a common placenta, which allows for the exchange of blood and hormones between the two fetuses through their fetal circulatory systems.

Identify the key factor: The male twin produces testosterone and other androgens, which can cross into the female twin's bloodstream via the shared placenta.

Explain the impact of androgens: The exposure of the female twin to male hormones during critical periods of development can interfere with the normal development of her reproductive organs, leading to masculinization and sterility.

Conclude that the freemartin condition arises due to hormonal influence from the male twin, which disrupts the female twin's normal sexual differentiation and reproductive development.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Freemartinism

Freemartinism is a condition observed in female calves born as twins with a male calf. The shared placenta allows for the exchange of blood and hormones between the fetuses, leading to the female developing masculinized traits and reproductive organs. This hormonal influence disrupts normal female reproductive development, resulting in sterility.

Sexual Differentiation

Sexual differentiation is the process by which the reproductive system and secondary sexual characteristics develop in an organism. In mammals, this process is influenced by sex chromosomes and hormones. In the case of freemartins, the presence of male hormones from the male twin alters the typical development of the female twin's reproductive system.

Placental Circulation

Placental circulation refers to the blood flow between the mother and the developing fetuses through the placenta. In cases of twin pregnancies, especially with a shared placenta, there can be significant mixing of blood. This can lead to the transfer of hormones and other factors that affect the development of each twin, as seen in the case of freemartins.

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